1. Field of the Invention
The invention relates to a multi-stage hydrotreating or hydrocracking process wherein reaction vapors are withdrawn between stages and replaced with hydrogen.
2. Description of the Prior Art
Hydrotreating and hydrocracking both involve catalytically promoted reactions between hydrogen and a liquid hydrocarbon. Hydrotreating is used primarily to remove nitrogen, sulfur, and other impurities in hydrocarbon feedstocks to other refinery processes. The hydrogen reacts with the nitrogen and sulfur contaminants in the feedstock to form ammonia and hydrogen sulfide. On the other hand, hydrocracking is typically used to upgrade refractory middle boiling or residual hydrocarbons. However, it too is a treating process since hydrogen combines with nitrogen and sulfur impurities in the hydrocracking feed and converts them to ammonia and hydrogen sulfide.
In accordance with Le Chatelier's principle the reaction rates of hydrotreating or hydrocracking may be increased by removing ammonia and/or hydrogen sulfide, as the case may be, from the reaction mixture. One method currently used to do this in hydrocracking is to carry out the process in two stages separated by a distillation. The effluent from the first stage is cooled and depressurized, reheated and fed to a distillation column, and the distillate is repressurized and fed to the following stage. In prior art hydrotreating processes multistage reactors were used with an interstage flash to remove ammonia and hydrogen sulfide. See, for instance, U.S. Pat. Nos. 3,159,564, 3,761,399, 3,907,667, 3,926,784, and 4,016,069.
A main object of the present invention is to provide a process for removing hydrogen sulfide and/or ammonia from a multistage hydrocracking or hydrotreating process that does not involve separate interstage treatment of the entire interstage effluents.